The present invention relates to metal working, and more particularly, to a method of producing hollow articles by deep drawing and a press for effecting same.
A better quality of hollow articles produced by deep drawing along with the provision of higly efficient equipment is quite essential where drawing of articles is effected with radial head pressure acting on the flanged portion of a blank.
There is known in the art a method of deep drawing of sheet metals wherein rigid pushers are used to act on the peripheral part of the blank in a manner to create radial head pressure affecting the flanged part of the blank. (USSR Inventor's Certificate No. 419,279, published in Discoveries, Inventions, Industrial Designs and Trade Marks Bulletin No. 10, 1974). In the process of drawing, the rigid pushers interact with the blank through their narrow sections which causes uneven distribution of head pressure over the peripheral portion of the blank. This, in turn, makes it impossible to increase the drawing coefficient K, which is determined by the relation of the blank radius R.sub.i to the punch radius R.sub.o. In addition, the method described above fails to provide radial head pressure required to act on the peripheral part of the blank in the drawing direction. As a result, the articles thus produced suffer from poor quality.
There is also known in the art a method of producing hollow articles by deep drawing, which resides in that the central portion of a blank positioned on a die is hermetically separated from the peripheral portion of the same blank, whereupon a high-pressure fluid is used to act upon the butt end of the blank peripheral portion, with the blank being drawn through the agency of a rigid punch (U.S. Pat. No. 3,495,433; cl. 72-347, published 1970). In the process of drawing, the pressure applied to the peripheral portion of the blank is brought down. This occurs due to a decrease in the diameter of the blank peripheral portion. However, at the initial stage of drawing the pressure tends to crowd the metal into a shape withut the punch participation, which results in an undesirable dome-formation in the central portion of the blank and, consequently, in a higher percentage of defective products.
The prior art teaches a press for the manufacture of hollow articles by deep drawing, which comprises a high-pressure vessel accommodating a die with a punch in rigid connection with a piston of a punch-actuating hydraulic cylinder, and a clamp formed with a collar provided to ensure hermetic separation of the blank central portion from its peripheral portion. The clamp is located opposite a drawing rib of the die whose end surface forms, together with the end surface of the clamp, a high-pressure annular chamber which accommodates the blank peripheral portion and communicates with a high-pressure chamber of an intensifier (U.S. Pat. No. 3,495,433; Cl. 72-347, published 1970).
The die is formed with a plurality of vertical grooves intended to communicate the annular high-pressure chamber with a pressure source. In its upper part, the die is fitted with a channel intended to communicate the die cavity through a return valve with the cylinder chamber into which a fluid, delivered along a line, is discharged. The cylinder is brought in contact with the high-pressure vessel to form an annular chamber wherein hydrostatic pressure of fluid is created to act on the peripheral portion of the sheet metal blank in the process of drawing.
This high hydrostatic pressure is not adjusted in the process of drawing, its value at the beginning and at the end of the drawing operation being very much in excess of a specified value. As a result, the formation of the peripheral part of the blank is effected spontaneously at the initial stage of drawing; thin-walled articles tend to wrinkle and thick-walled articles develop dents or hollows on their surfaces at the end of the drawing process.